The specific aims of the proposed series of studies are 1) to determine whether squirrel monkeys exhibit endogenous event-related potentials (ERPs) analogous to those associated with cognitive processing humans, 2) to subject such ERPs to neurophysiological and neuroanatomical analyses not possible in humans, and 3) to test the specific hypothesis that the noradrenergic locus coeruleus-to-neocortex projection system produces or modulates the production of the P300 ERP component in the monkey. We will extend our preliminary results which suggest that ERPs recorded from monkeys demonstrate endogenous components similar to those observed in humans. In one series of paradigms, cortical surface recordings will be obtained from monkeys presented with sequences of auditory and visual stimuli of the type that elicit N1-P2 and P300 potentials in humans. In a separate series, ERPs will be obtained from monkeys trained to perform in behavioral paradigms designed to be analogous to those in which humans demonstrate cognitively liabile ERPs. If and when potentials which are analogous in terms of behavioral and paradigmatic variables have been reliably elicited, we will determine the time-course and distribution of these ERPs in surface and depth recordings. We will also perform one and two-dimensional current source density analyses in order to localize the neural generators of these potentials. Additionally, using single neuron recordings, chemical lesions and electrical stimulation, we will test the specific hypothesis, suggested from our previous studies of the anatomy and physiology of the locus coeruleus-to-neocortex projection, that this system may play a role in the production of a late positive potential similar to the P300 observed in humans. The long-term objective of this research is to explore th neurophysiological substrates of human cognition.